Creatine kinase hydrolysis

The first observed product is the hydroxo-N-bound phosphoramidate complex, although there are almost certainly other intermediates. Both ester hydrolysis (to nitrophenolate ion) and transfer of a phosphate residue from O to N occur. An acceleration of at least 10 fold can be assessed for both processes, compared with the reaction of the uncoordinated ester with NH3 or 0H ion. The O to N transfer is a general biochemical occurrence, e.g. creatine kinase uses and creatine to transform ATP to ADP and form creatine... 

Affinity labeling ATP sites, 194-96 creatine kinase, 200-205 Amastatin, 94-96 Amide bond hydrolysis, 227 Amino acid sequences, renin inhibitors, 139,141f D-Amlno acids and activity,... 

Although it is true that abnormal proteins increase with age, most of them are a result of posttranslational changes. An example is the various isoforms of creatine kinase (CK). Here, the major isoenzyme, CK-MM (isoform CK-33), is normally synthesized in the heart and skeletal muscle. However, after its release into the circulation, carboxypeptidase hydrolyzes the terminal lysine from one of the M-peptides to form CK-32. Subsequent hydrolysis of the terminal lysine from the second M-peptide produces the third isoform, CK-3i (W8). Numerous similar posttranslational proteins are produced. Hence, the presence of abnormal proteins per se does not support this aging theory. 

The creatine synthesized in the liver is transported through the bloodstream to skeletal and heart muscle. It enters the mitochondria, where it is phosphorylated to crealine-P Creatine kinase catalyzes this reversible addition of a phosphate group, as shown in Figure 4.34. Creatine-P is unique in that its only known function is as an energy buffer. The creatine P formed in the mitochondria travels to the contractile proteins in the cytoplasm of the muscle fiber. The polymer, or complex, of contractile proteins is called a myofibril. Contraction of a myofibril is coupled to the hydrolysis of ATP to ADP. The immediate replenishment of ATP is catalyzed by a second creatine kinase, residing on the myofibril, that catalyzes the conversion of creatine-P to creatine. This reversal of the reaction takes place in the... 

Two pathways are possible for the acid hydrolysis of A -phosphorocreatine (44) to orthophosphate. Both pathways involve metaphosphate as an intermediate, but at pH > 1 creatine (45) is the major product, while at pH < 1 creatinine (46) is formed as the major product. This observation has led to the prediction that, in the creatine-kinase-catalysed phosphorylation of ADP by (44), metaphosphate... 

M. Perryman, D. Knell, and R. Roberts. Carboxypeptidase-catalyzed hydrolysis of C-terminal lysine mechanism for in vivo production of multiple forms of creatine kinase in plasma. Clin. Chem. 30 662-664 (1984). 

Phosphocreatine can be used as a phosphoryl donor for the synthesis of ATP in a reaction catalyzed by creatine kinase. Refer to Section 14.1.5 of the text for free energies of hydrolysis of ATP and creatine phosphate. 

Creatine is readily phosphorylated by ATP in a reversible reaction catalysed by creatine kinase. The standard free energy of hydrolysis of phosphocreatine is —43 kJ (—10-3 kcal) so the equilibrium favours ATP formation. 

Adenosine diphosphate (ADP) ADP is a substrate for ATP production, and a product of its hydrolysis. ADP stimulates respiration (oxidative metabolism) -breakdown of ATP increases ADP which in turn activates the processes which provide energy for ATP synthesis. In tissues such as muscle, much of the ADP is bound to macromolecules and therefore invisible to NMR. However, the free (and therefore metab-olically active) ADP usually present in only micromolar concentrations, may be deduced using the creatine kinase equilibrium (see above). 

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